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228
MORPHOLOGY AND EVOLUTION
some Chimpanzees, the Orang and the G-ibbons, the arch gives off the innominate (I.A.) and left subclavian (L.S.A.) arteries; and the former, after giving off the left common carotid artery (L.C.C.A.), divides into the right common carotid (R.G.C.A.) and right subclavian (U.S.A.; arteries. In one Chimpanzee I observed the
O.A
P.CA
FIG. 41.—The aorta and subclavian vessels in the Chimpanzee. A.A., aorta; A.B,, ascending branch; Ax.A., axillary artery; D.A., ductus arteriosus ; D.T.A., descending branch of transverse cervical artery ; I.A., innominate arfcery; I.M.A., internal mammary artery; L.C C^A. and R.C.G.A., left and right common carotid arteries; L.S,A. and R.S.A., left and right subclavian arteries; L.B.A,, left bronchial arfceiy; O.A., occipital artery ; P. A., pulmonary artery; P.O. A., deep cervical artery; S.A., spinal arteries; S.I.A. superior intercostal artery; S.S.A., suprascapulftr artery ; S.U.A., subscapular vessels ; T.A.A., thoracic axis : T.J.A., thyroidea ima ; V.A., vertebral artery ; a., subscapularis artery ; b., humeral circumflex trunk; c., artery to teres-major,
main left bronchial artery (L.B.A.) arising from the concavity of the arch. In many very young animals the ductus arteriosus (D.A.) is seen running from the arch to the left pulmonary artery. It is said that this vessel